Spark plugs are used in gasoline engines, gas turbines and some furnaces in order to ignite an air-gas mixture located in a combustion chamber by generating an ignition spark. Typically, a high voltage is generated by an ignition coil and said high voltage prevails on a central electrode of the spark plug and generates the ignition spark by jumping between the central electrode and a ground electrode that is arranged near to the central electrode.
The ignition voltage reaches the central electrode by way of an electrical resistance. This electrical resistance is typically generated in the interior of a ceramic insulator of the spark plug in that a powder is introduced into the insulator and is fused or sintered to become a resistor at that location by heating the powder. A sequence of different powders may also be used; for instance, a layer of powder having a comparatively low resistance may be followed by a layer with a higher resistance, whereupon finally a layer of powder having the low resistance is applied again. The layers of the powder having the low resistance improve the contact of the electrical resistor that is to be generated with the central electrode on one side and the connecting electrode on the other side of the resistor. The high expense of the procedure of introducing the powder into the insulator of the spark plug is disadvantageous in current production methods. In addition, current methods may not produce a reliable rate of product meeting quality specification tolerances.
The inventors herein have recognized the above challenges of producing a spark plug reliably and with minimal expense. The present disclosure therefore provides methods of producing a spark plug and/or a component of a spark plug, and provides a powder capsule which may enable a simplified, more reliable, and/or less expensive production method. In some examples, the powder capsule may ease materials handling during manufacturing and/or reduce a process cycle time.
A first aspect of the disclosure relates to a method for producing spark plugs, comprising providing a spark plug blank having an insulator that may comprise a hollow chamber that extends along a longitudinal axis of the insulator, arranging a central electrode in the hollow chamber of the insulator so that an end of the central electrode which may protrude beyond an end of the central electrode over a combustion chamber end of the insulator, providing a capsule filled with at least one powder, inserting the capsule into the hollow chamber of the insulator, arranging a connecting electrode in the hollow chamber of the insulator so that an end of the connecting electrode protrudes beyond a connecting end of the insulator, and heating the capsule.
Another aspect of the present disclosure relates to a capsule for use in producing a spark plug or spark plug component, such as a spark plug resistor or resistor assembly, wherein the capsule may be filled with at least one powder.
Another aspect of the present disclosure relates to a method for producing a spark plug resistor, wherein the method may comprise providing an insulator comprising a central cavity passing through the insulator. The method may further comprise providing a capsule, comprising a housing which becomes unstable when heated to a first threshold temperature, and further comprising one or more powders, which may fuse or sinter into an electrically resistive mass when heated to a second threshold temperature. The method may further comprise arranging the capsule in the central cavity of the insulator, compressing the capsule, and heating the capsule to heating the capsule to a threshold temperature exceeding each of the first and second threshold temperatures, such that the capsule is fused or sintered into an electrically resistive mass.
A production method in accordance with the present disclosure comprises the advantage that it is rendered possible to rapidly and reliably fill the hollow chamber of the insulator of the spark plug with the at least one powder. The amount of powder, and where required a desired layer sequence of powders, may be implemented in a simpler and more precise manner outside the insulator than within the insulator. It may be possible to inexpensively produce a spark plug by inserting a powder capsule into the insulator, and in the case of using multiple different powders, it may be possible by using a powder capsule to maintain a layer sequence of one or more powders or powder zones in a reliable manner.
The procedure may further comprise compressing the capsule arranged in the hollow chamber between the central electrode and the connecting electrode. The compressing procedure may increase the tensile strength of the powder that may be fused or sintered when heating the capsule and may lead to a more robust spark plug. In one embodiment, compressing and heating may be performed simultaneously. However, the compressing procedure may commence prior to the heating procedure and/or may be continued for some time after the end of the heating procedure, for example until the temperature falls below a predetermined threshold temperature.
A method in accordance with the present disclosure may further comprise producing or providing a capsule that may be filled with at least one powder. In one embodiment, producing the capsule may further comprise producing a capsule housing and/or filling the capsule with the at least one powder. The capsule may be manufactured in a two-part manner so that a capsule body may be filled with the at least one powder and may further be subsequently closed by a capsule cap. In one embodiment, the capsule may be a cassette, for example a wax cassette.
In one embodiment, a first region of a capsule may be filled with a first powder having a first electrical resistance and a second region of the capsule may be filled with a second powder having an electrical resistance that may be different from the first electrical resistance. In particular, the second region may be divided into a first part and a second part that may be arranged and spatially separated from one another on opposite-lying sides of the first region. In a further embodiment, the first electrical resistance may be greater than the second electrical resistance. The regions having the second powder may ensure a good contact between one or more of the electrodes and the first region having the first powder that has the greater resistance. The use of a capsule may offer particular advantages with regard to the expense of the method, especially in the case where different powders are layered and the layers may possibly be of different thicknesses.
The capsule housing may be manufactured at least in part from a material that may be unstable when subjected to heat above a threshold temperature. By way of example, the end faces and/or the peripheral surfaces of the capsule may be manufactured from the material that may be unstable when subjected to heat. Suitable materials may by way of example be a wax or a polymer. During heating of the capsule, the capsule may be heated to above this threshold temperature so that the material that may be unstable when subjected to heat becomes volatile, by way of example as a result of burning or evaporating.
The capsule housing may also be manufactured entirely or in part from a material that may be stable when subjected to heat at the temperature that prevails during heating of the capsule. For example, it may be feasible to manufacture the peripheral surface of the capsule from an electrically insulating material and to manufacture the end faces from an electrically conductive material. Where appropriate, it may be possible to select the material of the end faces or the temperature during heating of the capsule so that the material of the end faces melts and thus may contribute to providing a good contact with the resistive powder.
In one embodiment, the temperature during heating of the capsule may be selected so that the at least one powder may be sintered or melted during heating of the capsule.
Further aspects of the disclosure relate to a capsule that may be filled with at least one powder for use in the methods in accordance with the disclosure for producing a spark plug and a spark plug that may be produced according to the methods.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.